It is standard behaviour, nothing to worry about
If you do the Dark Elven Lords quest before you find Galadriel's phial, then you will receive the phial as a reward
If you do the quest after you find the phial, then you will get a random artifact light of similar power to Galadriel's phial (The random artifact light is always better, well, except if it has permanent darkness, 2 of my warriors got it with permanent darkness, and 2 of my rune knights got a unique cloak and not a cloak of stealth as a reward for the orc camp quest, I don't know if classes affect the quest rewards)
The same thing happens with Merry's cloak and the Barrow Downs quest

Sometimes you can kill the same orc unique (is it Golfimbul) twice, once in a random encounter and once in the Orc camp quest